This invention relates to a process for recovering organic material, primarily hydrocarbon liquids, from oil shale solids and is particularly concerned with a process for extracting the organic material from the oil shale at relatively mild temperatures.
Because of a dwindling supply of petroleum liquids from underground resevoirs, attention has recently been focused on the recovery of hydrocarbon liquids and gases from solids such as oil shale, coal, industrial and municipal solid wastes and the like. Work by both governmental agencies and private industry has demonstrated that the organic material in such solids can be converted with varying degrees of difficulty into volatile hydrocarbonaceous fluids such as combustible gases, motor fuels, heating and fuel oils, and various by-products which have value in chemical and petrochemical industries. In general, the more attractive of the recovery techniques previously proposed involve the heat treatment of such solids in a manner sufficient to distill or otherwise decompose the organic material into the above-mentioned volatile, hydrocarbonaceous products.
Oil shale is considered to be one of the best candidates of all carbon-containing materials for processing in such a retorting or pyrolysis scheme since it comprises a mixture of a minor amount of solid organic matter called kerogen and a major amount of mineral matter. The organic matter known as kerogen is a polymer which is virtually insoluble in organic solvents. Because of this insolubility, it has been virtually impossible in the past to extract the kerogen from the oil shale and therefore the application of heat via pyrolysis or retorting has had to be used. The retorting process is carried out at relatively high temperatures, normally between about 850.degree. F. and about 1000.degree. F., in order to cause the solid organic matter to undergo destructive pyrolysis and simultaneous conversion into liquid and light gaseous hydrocarbonaceous products with the remainder staying as a carbon-rich residue in the mineral matrix. Retorting, however, has several drawbacks. It is inefficient since only between about 60 and about 80 percent of the organic carbon is normally recovered, and at the high temperatures where retorting takes place, cracking reactions result in the formation of gas and undesirable carbon-rich residues which cannot be recovered. Furthermore, the process has a low thermal efficiency because of the high retorting temperatures required. Because of the disadvantages of the retorting process, it is highly desirable to be able to treat oil shales at lower temperatures to recover their organic matter in quantities comparable to those obtained via retorting.